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 6.9
 Center uni joint
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aussie 6.9

13 Posts

Posted - 03/11/2018 :  21:58:46  Show Profile  Reply with Quote
Could somebody give me advice on how to replace the center uni joint on a 6.9 please . Regards Mark

T.J. Woods

Australia
282 Posts

Posted - 03/12/2018 :  01:31:41  Show Profile  Reply with Quote
The best option would be to take it to a tailshaft specialist as the joint is staked in. Iíve heard of people having it modified to accept circlips with a bit of machine work,

Tim

1976 450SEL 6.9 #1432
1979 450SEL 6.9 #5866
1969 300SEL 6.3 #1394
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aussie 6.9

13 Posts

Posted - 04/05/2018 :  22:40:44  Show Profile  Reply with Quote
Thanks for that . Since you replied I have had driveline shop replace the uni but they have had two attempts at balancing the shaft and it still thumps at low speed under acceleration. Ok at high speed . They say they can't balance it at low speed . Any suggestions? The work has been done in Dubbo NSWr
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mgmg69

USA
6 Posts

Posted - 04/05/2018 :  23:57:32  Show Profile  Reply with Quote
Driveline troubles like this always are a drag.

Since you say you are getting "thumping" at slow speed when accelerate, I would say that the balancing of the driveshaft is not the issue. Sounds like you have either (1) a bad center support bearing or (2) bad u joint(s). You can visually inspect the center support rubber but of the bearing is bad it can bind. U joints should also be able to be felt when driveshaft is out if you try and articulate the u joint.

Balancing issues usually cause vibration at speed not thumping.

Hope this helps

450sel 6.9 Restore in Progress
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Aaron H

USA
479 Posts

Posted - 04/10/2018 :  12:37:08  Show Profile  Reply with Quote
Don't rule out a bad output shaft bearing in the transmission, either. When these wear out you'll get this low speed thump. As MGMG69 stated, low speed vibrations are not due to an out of balance. They're due to what all he mentioned. Center support bushing/bearing, universal joints, AND can also be due to bad flex discs. When the front flex disc is renewed, the rear one must always be renewed with it, as well. Be cautious about buying aftermarket flex discs. They often cause high speed vibrations.
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benzman70

USA
200 Posts

Posted - 04/10/2018 :  13:27:34  Show Profile  Reply with Quote
aussie, I had one that had defective rear subframe mounting bushings that let the rear diff pinion angle change under acceleration, causing the rear flex disc to wobble producing a thumping feeling.Replaced the subframe bushings and rear diff to body mount and problem went away.
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aussie 6.9

13 Posts

Posted - 04/19/2018 :  07:06:17  Show Profile  Reply with Quote
It seems that the driveline shop have damaged the shaft fitting the new uni. I have decided to order a new complete shaft which are available at reasonable cost. Will keep foum posted.
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aussie 6.9

13 Posts

Posted - 06/13/2018 :  06:22:31  Show Profile  Reply with Quote
New Dorman shaft has arrived. Yet to fit it.
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aussie 6.9

13 Posts

Posted - 08/16/2018 :  06:52:59  Show Profile  Reply with Quote
New shaft fitted and all is well.
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